1. Technical Field
The present disclosure relates to a method and an apparatus for treating a liquid with plasma.
2. Description of the Related Art
Techniques in which plasma is used for purifying or sterilizing a liquid or a gas have been studied. For example, there has been disclosed a sterilizing apparatus that produces active species such as OH radicals by using plasma and sterilizes water by using the active species.
A sterilizing apparatus described in Japanese Unexamined Patent Application Publication No. 2009-255027 includes a pair of electrodes. Upon a negative high-voltage pulse (2 to 50 kV/cm, 100 Hz to 20 kHz) being applied between the pair of electrodes, electrical discharge occurs. The energy of the electrical discharge causes water to evaporate and vaporize with shock waves, thereby generating a bubble containing water vapor. The electrical discharge generates plasma in the bubble.
In the sterilization method described in Japanese Patent No. 4408957, plasma is generated in or near a liquid whose pH has been set to 4.8 or less, and radicals produced by the plasma are brought into contact with the liquid in order to kill bacteria that are present in the liquid or on the surface of the liquid.
In the sterilization method described in Japanese Patent No. 5305274, plasma is generated in the gas phase by using a plasma generation device, ions are produced in the gas phase by the plasma, and an electric field is applied to the ions such that electrophoresis of the ions toward the liquid occurs. The pH of the liquid is set to 4.8 or less.